1. Field of the Invention
This invention generally relates to a stent. More specifically, the present invention relates to a stent comprising a stent body which is in particular used for expanding narrowed hollow vessels.
2. Background Information
Different types of stents are known from the prior art. These stents form a vascular prosthesis made from a physically compatible material. Stents are in general used for expanding hollow vessels, such as blood vessels or body orifices, and for keeping the vessels or orifices in an expanded state. To this end, the stent is normally positioned in its non-expanded state within a patient""s body inside a narrowed hollow vessel and is then expanded by suitable means, for instance a balloon catheter. The stent body normally consists of a web structure, which comprises a plurality of neighboring cells, each cell being defined by webs. During expansion the individual web portions of the stent are deformed, so that the portions permanently remain in the expanded form.
The problem of restenosis often arises in such expanded hollow vessels. After some time the portion of the hollow vessel which has been expanded by the stent is narrowed again. Such a restenosis may, inter alia, be caused by the inherent stiffness of the stent. As schematically shown in FIG. 6, the hollow vessel 10 is stiffened by the stent 1xe2x80x2. Strong irritations R of the vessel wall which result in a restenosis of the hollow vessel can in particular be observed on the two end portions of the stent due to the inherent stiffness of the stent body 2xe2x80x2.
In view of the above, there exists a need for a stent which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
One object of the present invention is to provide a stent that reduces the risk of restenosis in a hollow vessel in the area of an implanted stent.
Hence, according to the invention, there is provided a stent the wall thickness of which has been changed. This results in a stent having portions that due to the different wall thicknesses exhibit different inherent stiffnesses. Hence, the stent body within the portions of a reduced wall thickness has an increased flexibility, whereby irritations of the vessel wall at these places can be reduced or even be prevented altogether. Hence, the risk of restenosis in these portions can be reduced considerably.
Preferably, the wall thickness of the two end portions of the stent body is smaller than the wall thickness of a main portion of the stent body. As a consequence, the inherent stiffness of the two end portions of the stent body can in particular be reduced, so that the end portions exhibit an increased flexibility, whereby an abrupt xe2x80x9cdirectional changexe2x80x9d or a bending of the hollow vessel due to a different stiffness degree between the portion of the hollow vessel without stent and the portion of the hollow vessel with stent can be prevented. As a result, one obtains a more gentle transition between the hollow vessel and the stent, whereby a strong irritation on the end portions of the stent can be avoided.
According to a preferred embodiment of the present invention, the stent body comprises exactly one end portion having a smaller wall thickness than the remaining portion of the stent body. Such a stent can preferably be used in branches or rami of hollow vessels. The stent is arranged in the branched portion such that the end portion of a reduced wall thickness is oriented away from the branched portion. Hence, the stent portion is provided in the area of the branched portion or directly next to the branched portion with an increased wall thickness because the risk of irritations created by the stent is small on account of the natural extension of the branched portion in said area. In the area that is more remote from the branched portion, the stent, however, has a smaller wall thickness so that an increased flexibility of the stent is observed in said area and the stent can follow the natural course of the hollow vessel. Hence, the risk of irritations is reduced thanks to the high flexibility of the end portion of the stent.
To achieve a defined transition between the main portion and the end portion, which has a reduced wall thickness, the transition between said two portions is stepped or graded. As a result, the stiffness of the stent can be changed abruptly and the desired flexibility of the stent can be obtained in defined portions of the stent body.
To attain a gradual change in the stiffness or flexibility, respectively, of the stent body, the transition between the portion of an increased wall thickness to the portion of a reduced wall thickness is made continuous. The transition between the two wall thicknesses may e.g. be configured such that it is linear or exhibits a gradually changing increase.
To provide different inherent stiffnesses of the two end portions of the stent body, the wall thicknesses of the two end portions may be different. To provide a symmetrical stent, the end portions of the stent body may also have identical wall thicknesses. Furthermore, flexible end portions may also be achieved by identical or different lengths of the end portions in the axial direction or, in the case of gradually changing wall thicknesses in the transitional portion, by different axial lengths of the transitional portions.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the present invention.